Solvent extraction process



Patented Feb. 13, 1951 UNITED 25413380 SQLYENTiEXTRACIIQN= BBQGES S ffolvilleLlfPollyandClyde H. 0. Berg, Long Beach,

*"G'alifgas'signors to Union'Oil Company-of California, 1 Les Angeles, Gaiifl, ::.a qcorporation sof California "The presenti'invention relates toithe'separa- Ltion or gaseous hydrocarbon'mixtures, bmmeans Hofj'liquid selective, solvents, and 'relates rparticillarly to, separation of miXtliIBSjDf "hydroea'rbons ,ofr approximately-the same 'boiling point.

'ZIhe separation of" butadiene ffrom a 'mixture containingi butanes," butenes, and butadiene ifor "example, ,is--'..di'ii"1cult to accomplish by r ordinary methods of Ldi'stillationlbecause Ithere is only of the lowestl-boilingranfd highestboiling or these materials. ,-.Separ.atio,n ?;by solvent extraction,

. ther ef orc, off.ersa powerful molfor, segregation L0f $11Ch valuable; materials. asZ-buta'diene .orlbustenes ,fromzbutanes. IIt. .is: an g'objeot. of ,ourinvention to provide novel selective s olver1ts and o novelimprovements in the latter typeiof process.

I, The solvent extraction processes of this, invention may be applied to feed stocks consisting of mixtures of hydrocarbons having the same number of carbon atoms but :having differentldegrees ofxunsaturationior example, mix- :turesof ..membersiofmahorizontalg groupain the following atable:

i Degreefof Unsaturation of at on t r 1 Two Atoms None 1 One ,lGlefinS and I (Parafiinsh (Mono-claims) xapevtylanes) f i. ;2 ethanenwv v v acetylene. .,;L3.. propane, rriettligliacetylene.

ll a 19119. "Anew... .butanespn- ..b.utenes.inx q g pen a mass. 5. entanes pentenes "'{isoprene f p 7 methyl-nutmeg: dimethylacetyleneetc."

4 1-I0wever,'- the i above definition must :not :be: re-

;garded asjlimiting, the invention to: these specific -"Cla-ims. (Cl: 183-5115 -the-mi'ddle of the column, while the selective solvent is introduced near-the top-of the cclumn. --The-rafiinate gas,- which contains a larger proportion of the less unsaturated constituent than thefeed stock, rises through the upper part of the column countercurrent to the flow of liquid solvent and leavesfthe column-at the top while the.extract gas, which contains a larger proportionsof ,the more unsaturated constituent thanthe afiee'd stock, r,is .absorbed .by the,..solvent and. carried dcwnrtoather bottom of ;the .column A and out. ,The solventcontaining, the extract gas .risnintroduced .into .a ,clistillationcolumn, which pmayhe'eq il ed with a-reboilerv and-reflux cooler,

5 Candy-by the usual prooess-,of;. f-ractional distilla- -tion,: the extract gas 518 separated from the solvent in this column andeleaves the"column'at thetop. ,"Partof the-:extraota gas is returned to the base ofhthe'.extractionecolumn, and the re- :mainder passes "to storage. :Thebottoms, from 'zv the zdistillation column -are' -vpassed ithrough a :rcoolergpurifiedxif .necessary; :and -recirculated to sthetextraction column.

25 In'iia modificationx'of theabove:processithe-re- :of a portion ,;ofthe extract gas is accomuplished-withinthe:extraction' column byzthe: addition of; heatzatithe :base of the column: so: as td-boil ofi: a portion of -the extract gas from the 3 solven t. iAlthough"these-prooesses are preferred,

e other modifications r of the solvent 1 extraction process in which the selective solvents'of this in- '-'ve-r'1tion-may be employed are 'those" of: the' ex- 'tractive distillation type which has been-described for-example in U.'" -S. --Patent No." 1,948,777, --or "of other "conventional types used in liquid extraction of' gasecusmixtures.

As a specific example 70f an extraction carried out-"bythe "above preferred :method, "a mixture separations, for'it is ;v possible to separate byethe n i n v a l-m sh Weight 1113100858 "of ;-this invention y'ihydrocarbons of V the same degree or unsaturation, suchmast'lebutene .tfromr-l butene roraexample inywhichpairathe 2- ;-.b utene behaves -:as though it werezzmore ,nnsat- ,urated than 1 the sly-butane. :Materials .of c. three tdegreesucfl unsaturation, suchras-vinyl; acetylene v-.-,f.orv;ex ample, ..and cyclic hydrocarbons such .-as scyclopropane, or-.cyc1obutene, -,etc.;.-. ma-y. also be separated from other hydrocarbons of similar ;boiling ..point,

rAs an:examplesofiia solvenhextraetion process ,of this invention gaseous feedris introduced into @anextractionrcolumn (which may: bejpacked with lmaterials1whichmroyidelirnproved eontact uoh as,Raschigfrings plates, etc.) natqa, pointnear .55 the extract gas fromsthetsolvent, dethetlatter was recycled. Approximately equal volumes of rafiinate and extract gases were obtained per hour from the top of the extraction column and the distillation respectively, and these gases contained approximately 2% butadiene and 99% butadiene respectively. The same proces or the other modifications described above are applicable to separation of mixtures of butenes and butadiene, butanes and butenes, etc., or separation of other hydrocarbon mixtures as indicated previously, using the selective solvents of this invention.

The furfural water azeotrope used in the above process is a particular example of a preferred selective solvent according to our invention. The selectivity of this mixture as compared with that of 100% furfural is shown by the following data, which show what we shall call the selectivity ratio for the solvent, and define as the ratio of the volume of butadiene soluble at about 80 F. in the solvent to the volume of butane soluble underthe same conditions.

Selectivity The beneficial effect of minor proportions of water on the selectivity ratio of selective solvents is further shown by the fact that a 90% methyl ethyl ketone-% water azeotrope had a selec tivity ratio of 1.9 while a 100% methyl ethyl ketone solvent had a selectivity ratio of only 1.2; and a dioxane-water azeotrope water) had a selectivity ratio of 4.1 whereas pure dioxane had a selectivity ratio of 1.3.

It is an object of this invention to provide a number of selective solvents consisting of mixtures of more than one component, such as the above dioxane-water, which mixtures possess qualities of selectivity or operability superior to those of the major component. The azeotropes mentioned above, for example, are not only superior to the pure compounds in their selectivity, but have marked advantages in purification processes involving the use or presence of water, since the pure azeotrope is readily obtained on distillation of the mixtures. The azeotropes appear to be unique in their selectivity as compared with other mixtures containing slightly more or slightly less water. Solvents containing minor proportions of selectivity improving agents other than water are also included within the scope of this invention. Examples of such selectivity improving agents are polyhydric alcohols such as glycerine, ethylene glycol, diethylene glycol and other polyglycols, and the like; as well as low molecular weight amides such as formamide, acetamide, and other amides, preferably those containing less than about 5 carbon atoms. These may be used in place of water in the above selective solvents in any minor proportion in conjunction with selective solvents of the prior art or in conjunction with the novel selective solvents of the present invention as described below. For example, they may be used in place of water in the above furfural, dioxane, or methyl ethyl ketone solvents.

It is also an object of this invention to provide novel selective solvents for use in the extraction process of this invention, which solvents may be employed with or without, though preferably with, the above selectivity improving agents. Examples of these follow:

Nitroparafiins such as nitromethane, nitroethane, nitropropane, nitrobutane and the like are excellent selective solvents. Those are preferred which have less than about 5 carbon atoms, but cyclic saturated nitroparafiins, i. e., nitronaphthenes, such as nitrocyclohexane, nitrocyclobutane, nitrocyclopentane and the like may also be employed.

Mixtures of amines and phenols, which may be considered amine salts of the phenols are excellent solvents. The phenols may be phenol, cresols, xylenols, and the like. The amines may be methylamine, ethylamine, urea, ethylenediamine, or other amines preferably those containing less than about 5 carbon atoms. Examples are the urea salt of phenol, the methylamine salt of cresol, andthe like. These salts may contain a slight excess of either the amine or the phenol, though approximately equimolal proportions are preferred; and minor proportions of water.

Diketones such as acetonyl acetone, 2,3 -pentandione, 3,6-heptanedione, and the like are also excellent solvents, as are the unsaturated ketones whether acyclic such as methyloctenyl ketone, ethylhexenyl ketone, propylheptenyl ketone and the like, or cyclic unsaturated ketones such as isophorone, the cyclohexenyl ketones and the like. Acyclic saturated ketones having between about 4 and '7 carbon atoms are good solvents but are preferably used in conjunction with the selectivity improving agents shown above, since by themselves their selectivities are not as good as those of the above types. The above ketones, or a1dehydes of similar composition, i. e., the carbonyl compounds of this invention are preferably those which will dissolve at least about 3% by weight of water at 20 C.

Solubility data for some of the 4 carbon atom hydrocarbons in several of the above solvents follows:

Solubility at 8 0 E. in ml. of gas per ml. liquid solvent Se1ec Solvent tivity Buta- 2-bul-buisobun-budienc tene tene tene tane Furfuml 39 29 l. 3 91% Furfural- 9% H2O 26 19 14 14 7 3. 9 Methyl Ethyl Ketone, H10 67 36 1. 9 Acetonyl Acetone 38 11 3. 4 Nitromcthane 33 7 4. 7 Nitropropane-.- 70 25 2. 8

1 Azeotropic mixture.

In general, gases showing appreciable difierences in solubility in the selective solvent may be separated by the processes of this invention, the ease and completeness of the separation increasing with increasing differences in solubility, the more soluble gas being concentrated in the extract phase.

be made which W111 fall Within the scope of the following claims.

This is a continuation-in-part of our copending application, Serial No. 449,194, filed June 30, 1942, now abandoned.

We claim:

1. A process for separating one gaseous monoolefin from another gaseous monoolefin having the same number of carbon atoms which co1nprises contacting said mixture with a diketone and thereby selectively dissolving one of said monoolefins.

2. A "process according to claim 1 in which the diketone is acetonyl acetone. J

3. A process according to claim 1 in which the diketone is acetonyl acetone and the two monoolefins are 2-butene and l-butene.

4. A process according to claim 1 in which 2-butene is selectively dissolved and separated from l-butene.

ORVILLE L. POLLY. CLYDE H. O; BERG.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PA'IENTS OTHER REFERENCES Extraction of 1,3-Butadiene from Cracked Gases.

Comparative Solubilities of 1,3-Butadiene and Butenes, Moor et a1. U; 0. P. Co. Translation S-153, Feb. 6, 1942, pages 1-7. 

